(1) Field of the Invention
The present invention relates to an aqueous ink suitable for use in an ink-jet recording, in particular, an aqueous ink composition presenting a good quality as a color ink for a sheet of plain paper. This invention also relates to an aqueous ink composition which is preferably employed in an ink-jet printer, writing utensils such as ball point pens, marking pens and fountain pens, a recorder, or a pen-plotter.
(2) Description of the Prior Art
Recently, the ink-jet printer has been commonly used due to its advantages such as a low noise or a low running cost, and a color printer capable of being used for printing on the plain paper is also commercially available. However, in the conventional printers described above, all of requirements such as a regeneration of a color of an image, a waterfastness, a lightfastness, a dryness of an image and a reliable spread or discharge of the image can not be easily achieved. Particularly, in a case of the color printer, even if a degradation of the image would not occur in a printing unit for a particular color, for example, yellow, magenta or cyan, the image tends to degrade when more than two colors of red, green or blue are superimposed. In particular, when the image on the paper is dried without using a fixing unit, a permeability of the ink should be improved to aid the dryness of the image, as described in Japanese Laid-Open Patent Application No.55-29546. Without sufficient dryness, the image may too widely spread over the paper.
In Japanese Published Patent No.60-23793, it has been described that dialkyl sulfosuccinic acid may be a surfactant which can improve the dryness of the image and can cause less degradation of the image. However, dialkyl sulfosuccinic acid may cause disadvantages in that a diameter of a pixel of the image differs according to the type of paper used, a density of the image may significantly degrade, and the surfactant may be dissolved by alkali and lose its activity.
In Japanese Published Patent No.58-6752, a less-spreading and rapid-drying ink is described in which an ethylene oxide addition having an acetylenic linkage is used as a surfactant so that the permeability of the ink into the paper is improved. However, there may occur a problem in that the above-mentioned ink can not increase its rate of dryness when used with a direct dye such as DBK168 which has a hydrophobic interaction with the surfactant.
Furthermore, in Japanese Laid-Open Patent Application No.56-57862, another ink is described in which a strong basic substance is added to the ink. This addition of the strong basic substance may be effective in a case of acid paper being rosin-sized, but may not be effective in a case of the paper being sized by alkyl ketene dimer or alkenyl sulfosuccinic acid. The strong basic substance may not function well when two colors are superimposed on the acid paper.
A recording liquid is described in Japanese Laid-Open Patent Application No.1-203483, in which the recording liquid includes a polyhydric alcohol derivative and pectin. This liquid has pectin as a thickener so that an image is prevented from being spread and bled. However, there may occur a problem in that pectin is lacking a discharging stability after an interval during which printing is stopped, because pectin has a hydroxyl group acting as a hydrophilic group and is non-ionic.
On the other hand, in order to establish both the color-regeneration and the waterfastness on the plain paper, improvement of the dye per se is being attempted. However, it is not easy to achive a reliable dye whose waterfastness is also improved.
Applicants for the present application also have researched various magenta dyes and have developed a magenta ink which satisfies requirements for both the waterfastness and reliability in Japan Laid-Open Patent Application No.64-6237. However, the ink presents a tone of poor quality on the plain paper.